This invention relates generally to media printing systems. More particularly, the invention relates to a media printing system having an encoder that monitors the actual position of the media in order to control the firing of the printhead for the printing system.
Electronic label printing machines are often used to generate adhesive labels having images (e.g., indicia, graphics, art, specialized instructions, warnings, slogans, advertising, etc.) to facilitate identification, tracking and pricing of goods. Such label printers typically include: a printhead, an assembly (e.g., a label media cartridge) for supplying and feeding a label media past the printhead in order to be printed, a microprocessor, a read-only memory (ROM) programmed with appropriate instructions therein to operate the microprocessor, a random access memory (RAM), a keyboard with letter, number, and function keys for entry of alphanumeric information requisite to printing the indicia on the label media, and a visual display such as a Light Emitting Diode (LED) or Liquid Crystal Display (LCD) screen to convey information to a machine operator. These components function together to achieve the end goal of creating high quality and accurate labels from the label media using the electronic label printing machine.
Labels are made from a label media. The label media itself typically is made up of a roll of pressure sensitive tape that is attached, typically along a side containing an adhesive, to a continuous support roll of release liner material. The label media is fed in a media direction along a media path through the label printer. Discrete labels are formed by cutting the label media. Complex label shapes can be obtained by plotter cutting the tape layer only of the label media. The label media can be end cut (i.e., cutting through the tape and the release liner layers) or portioned into an end cut label media portion in order to obtain as many discrete labels in a continuous row as is desired. In other words, one or more than one discrete label can reside on an end cut label media portion. An end cutting operation can occur with or without a plotter cutting operation first having taken place. Following label media cutting, the discrete labels can be removed from the release liner and attached, as appropriate, to the particular application requiring identification. Since there are many types of label applications, there are many combinations of tape and release liners that can provide labels of varying sizes, colors, formats, and characteristics.
One type of label printer employs a thermal transfer printhead. In general, the use of thermal printheads in label printers has increased as the quality and accuracy of thermal printheads has improved. Thermal transfer printing uses a heat-generating printhead to transfer an ink, or the like, from a thermal transfer ribbon to a label media to form a label image on the media. A microprocessor determines a sequence of individual thermal, typically resistive, printhead elements to be selectively heated or energized. Energizing the sequence of elements in turn heats the ribbon so as to transfer the ink from the ribbon, creating the desired image on the label media, and specifically, on the label tape. The label printer can be fed label media from a label media cartridge. Simultaneously, a thermal transfer ribbon can be fed from a ribbon cartridge. While the label media runs between the printhead and a support (platen) roller, the transfer ribbon can run between the printhead and the support roller. Thus, the label media and the transfer ribbon can run together in an overlay relationship between the printhead and the support roller.
When it is desired to print a color image on a label media, it is generally required to print the image by passing the label media several times past the printhead. To accomplish each pass, the label media is fed, retracted, and then re-fed again past the thermal printhead. With each pass, a different primary color, for example, in a traditional color scheme, cyan, magenta, yellow, and black, is printed from a continuous ink ribbon onto the label media using the printhead. In this manner, based on the amount of each color printed, a composite color image can be printed onto a label media.
It is desirable to be able to track the position of the media. In prior systems, the position of the media is dependent upon the step resolution of the motor that controls the position of the media. By monitoring the motor, consequently, the position of the media moved by the motor can be identified. However, because of problems such as media slip within the transport mechanism, the media may become offset from the motor controlling the movement of the media. The result is a print defect in the output of the printing system, particularly when there is no feedback to a control microprocessor that slip has occurred.
Even in those systems in which positioning of the media is determined by monitoring the media, generally any information obtained is used to control the speed of a drive motor that is connected to the platen on which the media is travelling. The position of the media does not correspond to any printing operation.
Therefore, it would be desirable to be able to track the print media directly and send signals based upon the positioning of the media and generate a signal that results in firing a thermal printhead, therefore bypassing any irregularities in the media positioning system.
An invention is disclosed that overcomes the aforementioned problems, and provides a direct media monitoring/printing system. In one aspect of the invention, a method of determining the position of a label media and printing to the label media based on the label media position is disclosed. The method includes using an encoder to track the position of the label media. As the label media advances during printing, an encoder shaft rotates with an encoder traction roller upon which the label media rides. As the encoder shaft rotates, optical reflections that occur within the encoder are interrupted, each interruption corresponding to a desired media travel distance. When the optical reflection is interrupted, the encoder sends a signal to the controller, which then sends a control signal to fire the printhead, and consequently the label media is thermally printed. The system is useful in thermal printer systems to provide more accurate position information of the label media, and consequently, more accurate printing. In this manner, with the encoder tracking the motion of the media, the timing of the printing of the label media is determined upon the actual position of the label media itself.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.